This invention relates to a method of inspecting the outer form or appearance of a bonding wire bonded onto a semiconductor and an apparatus used for working of the method.
In recent years, according as semiconductor elements such as ICs, LSIs, COBs (chips on board), etc. have been highly integrated, and the quantity of productions has been increased, a method and an apparatus for carrying out inspection of the outer appearance of bonding wires connecting chips to package frames or boards in these semiconductor element highly integrated have been developed to find out wiring and ball defects such as broken or too close wires and incorrect wiring paths.
In such bonding wire inspection method and apparatus, it is required to inspect precisely the three-dimensional outer appearance of the bonding wires.
This kind of method and apparatus are disclosed in Japanese Patent Laid-Open Publication (Japanese Kokai) No. 139638/1984. In the conventional method and apparatus, there is provided a table movable horizontally and vertically for supporting a semiconductor as an inspection object. Over the table is disposed a camera which has a lens with a small focal depth and captures image of bonding wires on the semiconductor to send video signals to a signal processing unit.
The table for supporting the semiconductor is moved vertically little by little within the entire range of the semiconductor in its height direction. That is, the table is, firstly, stopped at a first position where the top portion of a bonding wire having a curved shape coincides with the focal point of the camera. At this time, an image at the top portion of the wire is displayed clearly or brightly with other portions thereof displayed dimly. Secondly, the table is moved slightly upwardly to stop at a second position where a portion of the wire slightly lower than the top portion thereof coincides with the focal point of the camera, resulting in that an image at a portion of the wire lower than the top portion thereof is displayed brightly with other portions thereof including its top portion displayed dimly. In this manner, the semiconductor as an inspection object is gradually moved to change the relative position between the focal point of the camera and the curved shape of the wire thereby to capture an image of portion of the wire which is located at position in focus. These images thus obtained are processed by the signal processing unit to recognize the three-dimensional shape of each bonding wire. Instead of the table, an optical system in the camera may be operated to change its focal point.
The above method and apparatus can be theoretically carried out and manufactured, respectively.
However, in this conventional method and apparatus, the table for supporting the semiconductor thereon or the optical system of the camera must be moved precisely intermittently to stop at a several of different positions within a small range corresponding to the height of the inspection object.
Therefore, the conventional method and apparatus is not fully satisfactory at present.